This invention relates to the bending and tempering of thermoplastic sheets such as glass plates that pass through a shaping bed made up of straight rollers or curved rods placed along a curved profile and it relates particularly to an installation whose curved profile can easily be adjusted and modified.
French patent publication No. 2,442,219 describes the bending and tempering of glass sheets while they advance through a shaping bed comprising straight rollers or curved rods mounted in a curved profile. The glass sheets, which previously have been heated to their softening temperature, gradually take the shape of the shaping bed on which they advance. They acquire a simple curve in the lengthwise direction of their advance if the shaping bed is made of straight rollers. If, however, the bed is made of curved rods tilted by pivoting around the shaft that goes through their ends, as disclosed in U.S. Pat. No. 4,292,065 which is incorporated herein by reference, the sheets acquire a double curve. In addition to the lengthwise curve caused by the lengthwise curved profile of the shaping bed, the sheets also acquire a crosswise curve due to the shape and tilt of the curved rods.
As taught in French patent publication FR No. 476 785, the bearings of the rollers or curved rods and all the other elements such as upper holding rollers, counterrods and blowing nozzles in the tempering zone are advantageously mounted on spring blades whose curvature can be adjusted by tension rods connected to the ends of the blades. With this system, however, it can be difficult to obtain a uniform and reproducible curve since the loads supported by these blades can alter the elasticity and modify the curvature of the blades locally and since the unit can vibrate, especially because of the air blowing from the blowing nozzles during tempering.